The present invention relates to a cooling arrangement, particularly for cooling electrical devices with water-cooled electric conductors with deionized cooling water and a closed cooling system which contains a main loop and at least one parallel loop contaning a mixed-bed filter.
For cooling electrical devices having high power rating, for example, generators and travelling-field tubes as well as heavy-duty cables, closed cooling systems are provided, as is well known, which contain cooling water low in ions, so-called deionate. The cooling water flows through the current-carrying conductors of the device which generally consist of copper or copper alloys.
For cooling especially sensitive cooling points, for example, cooling heads and seals of the boiler circulating and boiler feed pumps in power generating stations, secondary loops are provided, as also is well known, which are likewsie constructed as closed cooling loops and may be provided with a mixed-bed filter. In order to maintain the electrolyte content in the cooling system as low as possible, a small partial stream of the cooling water, which may amount to about 0.5 to 5% of the volume of the water, can be conducted through a parallel loop which contains the mixed-bed filter. In such a cooling system, the cooling water acquires a very low electric conductivity which may be lower than 1 .mu.S/cm. Part of the copper or the copper alloy can be removed by the cooling water through corrosion and deposited elsewhere or in following parts of the system. The corrosion removal rate depends on the pH-value of the cooling water and decreases with increasing pH-value. The pH-value has therefore, been raised in secondary cooling loops of power generating stations by the addition of sodium hydroxide to a value of at least 9. (VGB-Kraftwerkstechnik 59, September 1979, pages 720 to 724).
The existing mixed-bed filter which has, as is well known, the purpose to filter metal ions, for example, copper, nickel and iron ions and anions, for example, HCO.sub.3.sup.- ions, out of the cooling waters, is an obstacle to alkalizing the cooling water in the cooling system. The mixed-bed filter generally contains a hydrogen loaded cation exchanger and a hydroxide loaded anion exchanger. If an alkalizer is used, the cations of the alkalizer are filtered out of the loop again by the cation exchanger of the mixed-bed filter. A predetermined pH-value thus can be maintained only by continuous addition of alkalizer and, hence, the cation exchanger is consumed and must be renewed correspondingly more often.